Abacavir (brand name Ziagen) is used in the treatment of human immunodeficiency virus (HIV) infection. Abacavir is a nucleoside (and nucleotide) reverse transcriptase inhibitor (NRTI), and is used in combination with other medications as part of highly active antiretroviral therapy (HAART) (1).
Hypersensitivity reactions associated with abacavir can be severe and potentially fatal. Symptoms include fever, rash, vomiting, and shortness of breath. They typically appear within the first 42 days of treatment (11 days median onset).
HLA-B*57:01 significantly increases the risk of hypersensitivity reactions when abacavir is administered. Approximately 6% of Caucasians and 2-3% of African Americans carry this allele in the human leukocyte antigen B (HLA-B) gene. The HLA-B gene plays an important role in how the immune system recognizes and responds to pathogens, and mediates hypersensitivity reactions. HLA-B*57:01 has been found to be associated with abacavir hypersensitivity across different ethnicities, including Caucasians, Hispanics, and individuals of African origin (2, 3).
Screening for the HLA-B*57:01 allele before starting abacavir therapy is recommended for all patients according to the FDA drug label for abacavir (Table 1). Even if previously tolerated, screening should happen before restarting abacavir therapy if HLA-B*57:01 status is unknown. Abacavir is contraindicated in HLA-B*5701-positive patients, and in patients with a prior hypersensitivity reaction to abacavir. Dosing guidelines from the professional societies, Clinical Pharmacogenetics Implementation Consortium (CPIC) and the Dutch Pharmacogenetics Working Group (DPWG) of the Royal Dutch Association for the Advancement of Pharmacy (KNMP), also recommend that HLA-B*57:01 screening should be performed prior to initiation of abacavir therapy and an alternate drug be administered for patients with the allele (Table 2, Table 3)(1, 3-5).